Load the Debian 13 VM hardware from QEMU config files

Move the Debian launcher's QEMU arguments into qemu/debian13.ini, which
the launcher renders with the per-run file paths and passes to QEMU with
-readconfig, followed by qemu/debian13-<arch>.ini for the machine type
and arm64-only devices. Memory, CPU count, SSH port and accelerator are
now set in the config files, replacing VM_MEMORY, VM_CPUS and
VM_SSH_PORT; VM_QEMU_CONFIG selects a different shared config file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YKxXLyiL7XJ3a9e8HmR2my

README.md

@@ -22,8 +22,18 @@ background while still showing the graphical window:
 The launcher uses KVM when `/dev/kvm` is accessible, forwards host port `2222`
 to guest port `22`, and creates `.vm/debian13/disk.qcow2` as a 20G writable overlay with the
 original qcow2 image as its backing file. The base image therefore stays
-unchanged. Resource settings can be overridden with environment variables;
-run `./run-debian13.py --help` for the full list.
+unchanged. Run `./run-debian13.py --help` for the supported environment
+variables.
+
+The Debian VM hardware (accelerator, 8G memory, 8 CPUs, drives, network) is
+defined in the QEMU config file `qemu/debian13.ini`; the machine type and
+architecture-specific devices are in `qemu/debian13-amd64.ini` and
+`qemu/debian13-arm64.ini`. Edit these files to change the settings. The
+launcher fills in the `${...}` file path placeholders of `qemu/debian13.ini`,
+writes the result to `.vm/debian13/qemu.ini` and starts QEMU with
+`-readconfig` for that file followed by the one for the guest architecture.
+QEMU arguments given after `--` override the config files, for example
+`./run-debian13.py -- -m 4G -smp 4`.
 
 The launchers accept `--state-dir DIR` to keep
 the VM disk, seed ISO, UEFI variables, PID file and console log in `DIR`